1. Field of the Invention
The present invention relates to a hand-held drive-in tool for driving fastening elements and including a guide, a driving ram for driving fastening elements such as, e.g., nails or bolts, in a workpiece and displaceably arranged in the guide, a drive unit for displacing the driving ram and having a safety element, a press-on element for controlling the safety element of the drive unit, and spring means for biasing the press-on element in a drive-in direction.
2. Description of the Prior Art
The drive unit of the drive-in tool of the type described above can be formed as a mechanical, electrical, pneumatic unit or be operated by combustion power.
U.S. Pat. No. 4,375,867 discloses a drive-in tool of the type described above. The drive-in tool includes a driving ram for driving in nails and which is advanced by an electrically operated solenoid. The safety device includes a stirrup spring with a control cam surface for engaging a projection provided on a trigger switch. The spring is formed at an end of a rod-shaped press-on element displaceable in a guide located in the housing of the drive-in tool. The spring serves as a safety element that provides for actuation of the trigger for initiating of the setting process only then when the drive-in tool is pressed with its mouth against a workpiece. The displaceable press-on is resiliently supported in the housing by the stirrup spring.
The drawback of the known drive-in tool consists in that the biasing force with which the press-on element is biased out of the housing, i.e., in the drive-in direction is always the same, independent of the orientation of the drive-in tool relative to the gravity force, i.e., when the drive-in tool is oriented with its mouth in the direction of the gravity force (e.g., for driving nails into a floor), and when the drive-in tool is oriented with its mouth in a direction opposite the direction of action of the gravity force (e.g., for driving nails into a ceiling). At driving of nails in the direction of gravity force, it is easier to overcome the gravity force because the mass of the drive-in tool contributes to overcoming of the gravity force, whereas at driving nails in the opposite direction, the press-on force should be noticeably greater because additionally to overcoming the gravity force, the mass of the drive-in tool should also be displaced in a direction opposite the direction of action of the gravity force.
The object of the present invention is to modify a drive-in tool of the type discussed above so that the above-mentioned drawback of the known tool is eliminated, and that a relatively uniform press-on force needs to be applied thereto independent of the orientation of the drive-in tool relative to the vector of the gravity force.